Size-induced d band center upshift of copper for efficient nitrate reduction to ammonia

Electrocatalytic nitrate reduction (NO₃RR) technique has emerged as a hotspot in NH₃ production, for its practicability, and a series of advanced electrocatalysts with high activity and robust stability needed to be constructed in today's era. In this work, size-tunable Cu nanoparticles on porous nitrogen-doped hexagonal carbon nanorods (Cu@NHC) were reasonably designed and served for catalyzing NO₃RR in neutral media. Especially, Cu_30%@NHC demonstrated a remarkable electroactivity for NH₃ production as it showed a suitable grain size with massive catalytic centers and favorable d band structure with faster *NO₃^--to-*NO₂^- catalytic dynamics. As expected, Cu_30%@NHC (3628.28 µg h^-1 mg_cat.^-1) had a much higher NH₃ yield than those for Cu_20%@NHC (1268.42 µg h^-1 mg_cat.^-1) and Cu_40%@NHC (725.03 µg h^-1 mg_cat.^-1). And those collected NH₃ products indeed derived from NO₃RR process revealed by ¹⁵N isotope-labeling and systemic control tests. Moreover, Cu_30%@NHC was also durable for NO₃RR bulk electrolysis with minor loss in activity. This work offered an effective modifying tactics to boost NO₃RR catalysis and could guide the design of other advanced electrocatalysts via size-induced surface engineering.